Econometrics

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Commonly econometricians conduct inference based on covariance matrix estimates which are consistent in the presence of arbitrary forms of heteroskedasticity; the associated standard errors are referred to as “robust” (also, confusingly, White, or Huber-White, or Eicker-Huber-White) standard errors. These are easily requested in Stata with the “robust” option, as in the ubiquitous

reg y x, robust

Everyone knows that the usual OLS standard errors are generally “wrong,” that robust standard errors are “usually” bigger than OLS standard errors, and it often “doesn’t matter much” whether one uses robust standard errors.  It is whispered that there may be mysterious circumstances in which robust standard errors are smaller than OLS standard errors. Textbook discussions typically present the nasty matrix expressions for the robust covariance matrix estimate, but do not discuss in detail when robust standard errors matter or in what circumstances robust standard errors will be smaller than OLS standard errors. This post attempts a simple explanation of robust standard errors and circumstances in which they will tend to be much bigger or smaller than OLS standard errors.

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This post briefly surveys some of the methods and results in the literature on health and income inequality, closing with some remarks on problems with the existing literature and where future research may take us. It is not intended as anything resembling a comprehensive survey; Lynch et al (2004) provides a useful review of the empirical literature up to that time.

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Yesterday Federal Agricultural Minister Gerry Ritz uttered insane lies about dairy supply management:

I would make the argument that I don’t see those inflated prices, certainly, depending on where you buy,” Ritz told a joint news conference with Alberta Agriculture Minister Evan Berger and Saskatchewan Agriculture Minister Bob Bjornerud.

I received a flyer in my mailbox last night when I got back to my apartment and I opened it up and it’s from Canadian Tire. They’ve got four litres of milk for $4.19. That’s completely comparable to the American price that we’re always being beat up over.

Canadian Tire Econometrics aside, consumers are of course harmed by high prices driven by quantity restrictions. Click here to see a graph showing how much higher our prices are than the EU, US, or New Zealand (all of which all of which except New Zealand [*] also have some sort of supply management, Canada’s is just more severe).
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Antibiotic overuse causes great social harm yet is largely absent from public discussion of drug policy. There is a textbook external effect of an antibiotic prescription: the more antibiotics are used, the higher the risk we all face of resistant infections. As a result, there tends to be too much use of antibiotics. There have been ongoing efforts to reduce use of antibiotics, particularly in the context of treating respiratory infections, in part by educating GPs, the supply side of the relationship, on appropriate use.

In “Patient knowledge and antibiotic abuse: Evidence from an audit study in China” Janet Currie, Wanchuan Lin, and Wei Zhang consider the demand side of the relationship: what is the effect of patient knowledge on antibiotic use? Read the rest of this entry »

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Say you wish to estimate a model with a binary dependent variable. You recall that you ought not use OLS primarily because OLS will not bound your predicted values between zero and one. So you use a nonlinear variant, say, probit. But you also recall that it doesn’t matter much if you just use OLS and ignore the binary nature of your dependent variable so long as you are interested in estimating the effects of your covariates, not generating predicted values.
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Frances Woolley has posted some great tips on how to clean data in Stata. This post follows up with some tips on how to quickly and robustly estimate models as you vary specifications, and on how to get your results in a publication-ready form. The .do file described in this post can be downloaded by clicking here, you must change the extension from .doc to .do.

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